1. Field of the Invention
The invention relates in general to low power air conditioning systems, and, in particular, to a low power air conditioning system employing a tube and shell heat exchanger for use in arid conditions.
2. Description of the Prior Art
The provision of air conditioning for structures that are located in arid, high temperature deserts is essential to enjoying a good quality of life, and, in some instances, is essential to supporting life. This is true for both humans and livestock.
In desert environments, daytime temperatures often reach well above 100 degrees Fahrenheit while at the same time the relative humidity is often below 20 percent. Typically, conventional evaporative cooling based air conditioning systems, so called “swamp coolers”, are effective in such conditions, because of the low humidity. A source of electrical power is required to operate such systems, so the cost of operation is a limitation on their use. Conventional evaporative coolers consume considerable quantities of water so their use is limited to areas where water is available. Sufficient quantities of water are not always available in desert environments. Other types of air conditioning systems require the use of refrigerants, sealed buildings, expensive and high maintenance equipment, and are expensive to operate. Some dwellings and particularly buildings in which livestock may be kept are not well sealed or insulated so there is little impediment to the interiors of such structures reaching thermal equilibrium with the exterior environment. Typically, such structures are not provided with air conditioning systems because of the cost of operating them and the general ineffectiveness of air conditioning systems in such structures. Most air conditioning systems operate on electricity, and electricity is not always available, or is not available at a reasonable price where the structures are located. It would be greatly beneficial to both human beings and livestock if an effective, simple, self-contained air conditioning system could be provided for desert environments that would operate inexpensively in unsealed structures.
In its simplest form evaporative cooling of buildings has been accomplished by injecting a fog or mist of water into a moving stream of air. See, for example, Atkins, U.S. Pat. No. 5,146,762. One problem with this system is that it causes excess humidity within the building resulting in algae and bacteria problems. Atkins proposes to minimize some of these problems by placing exhaust fans at one end of a building widely spaced from fogger nozzles at the opposite end of the building. The disclosed rate of water consumption is very high. In excess of 95 percent of the water supplied to the fogger nozzles is consumed. Atkins' evaporative cooling system is said to produce a temperature drop of approximately 20 degrees.
Conventional evaporative cooling systems have been combined into more elaborate systems that include heating means. See, for example, Grant et al. U.S. Pat. No. 4,773,471. Conventional evaporative cooling systems have also been combined into elaborate systems with refrigerated air systems. See, for example, Conner U.S. Pat. No. 5,911,745.
Urch U.S. Pat. No. 6,434,963 discloses an air cooler with two air flow paths, namely, an inlet path for outside air and an outlet path for stale air. A heat exchanger pre-cools the fresh air with heat extracted from the stale air, and further cooling is achieved by means of an evaporative cooler that spans the two air flow paths.
Those concerned with these problems recognize the need for an improved air conditioning system.